As little as nothing. $0. Just download the new version and type in your key. It's that easy.
I do charge a nominal fee to cover my costs if you want me to ship a new diskette and/or manual. See the order form that GIFConverter will print out for you.
When I was developing GIFConverter in the late 80's, I became frustrated with a software company that was charging for upgrades. Whatever version I had came with bugs. I'd pay for an upgrade, and it'd fix some bugs and introduce new ones.
I decided that's not the way I wanted to run my business.
You see, all software has bugs. My software has bugs. Even big industry software from name brand corporations has bugs. I don't believe that you should have to pay for it when I fix my mistakes. If you're happy that I fixed a bug and GIFConverter is once again useful to you, and you want to somehow pay me back for it, do this: Tell a few friends about it.